Storage devices such as a magnetic medium based disk drive can store data on circular, concentric tracks on a disk surface. A magnetic medium based disk drive can include one or more bit-patterned media (BPM) based disks. BPM based disks have separately defined bit positions. In some implementations, a BPM based disk includes an ordered array of uniform magnetic islands where each bit occupies a single magnetic island.
A disk drive uses one or more clock signals for drive operations such as read and write operations. A drive head, in the disk drive, retrieves and records data on a rotating disk as the head flies on a cushion of air over the disk surface. When retrieving data, magnetic field variations are converted into an analog electrical signal, the analog signal is amplified, converted to a digital signal, and interpreted. A drive head can include a read head and a write head.
To guarantee the quality of the information saved on and read back from the disk, the drive head should be accurately positioned at the center of the track during both writing and reading, and the speed or frequency of read and write should be accurately controlled with respect to the rotating disk. A closed-loop control system can respond to servo information embedded in dedicated portions of a track on the recording surface to accurately position the head and synchronize the timing of drive operations.